People have forgotten guns and knives in their luggage that TSA has confiscated, and TSA proudly advertises those numbers. What is noticeably absent is information about any attacks TSA has thwarted. Of course it's possible some attacks have been prevented by deterrence but I doubt that as TSA has a 95℅ failure rate detecting explosives and other weapons[1].
[1] http://www.nbcnews.com/news/us-news/investigation-breaches-u...
Slate has another article from 2010 you might enjoy http://www.slate.com/articles/news_and_politics/explainer/20...